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1" PVC to 3/4" PVC when do I reduce it?

I hired someone to set this up for me, but i'm not sure they are qualified. I'm in San Diego. The main line from city is 3/4". The pressure on my hose faucet is 55 PSI. He has already run the 3/4" city line to a Tee 1" PVC to my control valves. It looks to me that the 1" main PVC line running to the control valves (Orbitz 3/4") has been reduced to 3/4" using some sort of black colored reducer (not sure)? I have 5 zones. Zones 1 and 2 are for grass at the same elevation. Zones 3,4 are for sprinklers on a slope and Zone 5 is drip irrigation for the slope. The same black reducer/backflow preventer is on the zones 3,4,5.
The set up just looks odd to me. I still have time to make corrections, but thinking of calling a professional to look at the set up prior to having everything buried. What do you all think. Is it ok to reduce the 1" to 3/4" PVC prior to the controller valves? Or should the controller valves all be 1" and then reduced to 3/4" PVC AFTER the controller valve? I'm a bit lost...newbie here. Please see picture (sorry only lets me post a 20kb size photo =that means its super small, will try to find out how to post larger picture).
So the first black device on left reduces the 1" to 3/4". The second black device on zone 3, is all 3/4". Is this a backflow preventer? Sorry could only fit zones 1-3 in the picture.

updated picture

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Update: added larger photo of valves. I found out that the black connection is a Dig 45 Backflow preventer (according to sticker on it). I think it is uneccessary to have off the 1" main to the control valves. I don't see an issue with having it (after control valves)for zones 3,4,and 5.
Another question. Should I put a pressure reducer for zone 5 drip line? I have a 25PSI pressure reducer that I can have him install on zone 5 post-valve.
Any help would be appreciated. Thanks.

The controller valve set up is on flat ground. Zones 1, and 2 are flat ground(same level as control valves), zone 3,4, 5(drip) are on an elevated slope. I don't think these are the correct backflow devices to use (black connectors). I already had him remove the one from the main line since it was leaking. I think these backflow devices are used for drip systems with a fertilizer system to prevent it from flowing backwards. I'm not sure why he used them on zone 3,4, and 5. Am I correct that it won't cause a problem if i leave it in there (currently not leaking)?

I'm not going to comment on the elevation differential. I do have a couple of observations though.
I'm assuming the device you removed is there on the left of the manifold. That should have never been installed.
Whoever installed this does have a very good eye. I'll give them an A for symmetry. I'd hire them.
I saved the picture to my computer so I could zoom in on it better. I don't see much glue on the manifold fittings. Time will tell if there's enough.
The valve on the right. That's valve 5 I'm assuming. Why is the filter so low to the ground? It's only a couple of inches from the lateral line.
Are the pipes only 3 inches under the ground or are you going to bury the filter? Or both. Does the dripline require a pressure reducer? Where is it?
You already have anti-syphon valves. You don't need those black things at all. He might have those things in there because the valves are lower than the sprinklers and maybe the black things will keep the valves from draining too much. They look like they're in a good location for draining though. Oops I guess I did comment on the height difference. I'm still not going to say they're not up to code because of the height of the valves.
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Why is the filter so low to the ground? It's only a couple of inches from the lateral line.
Are the pipes only 3 inches under the ground or are you going to bury the filter? Or both. Does the dripline require a pressure reducer? Where is it?
You already have anti-syphon valves. You don't need those black things at all. He might have those things in there because the valves are lower than the sprinklers and maybe the black things will keep the valves from draining too much. They look like they're in a good location for draining though. Oops I guess I did comment on the height difference. I'm still not going to say they're not up to code because of the height of the valves.
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I don't know why the filter is so low to the ground on Zone 5. Our water is pretty clean here in San Diego, but it would have been nicer to have the filter higher. I belive it will be about 3-4 inches buried. The area is gravel on the side of the house so draining shouldn't be a problem.
The dripline pressure reducer is not installed yet. I was thinking of putting it in where it feeds out at the top of the slope to minimize pressure loss (water traveling up the 25 foot slope).
I think the black backflow preventer are there for the slope, but they are not working very well since it is leaking water (from lines feeding the slope) from the control valve when turned off. Everything works fine when turned on (no leakds from control valve. When I turn on the system, I do hear air coming out of the sprinklers on the slope. Is there a better check valve I can put here (HC-75F-75M) and remove the black D45 Dig Backflow preventer? Is it a big problem to have water draining from the control valves from the slope?

Elevations completely change the rules. You do not use antisyphon valves to feed lines that flow to points uphill. Also, in any event, you do not install check valves downstream of antisyphon valves.

The equipment shown in the photo screams Amateur Hour to me.

So your recommendation is not to use check vavles downstream of the antisyphon valves. After reading this board, I have seen recommendations to run the main line from the street up to the top of the slope and locate the valves at the top of the slope (highest point), but this poses logistical problems with power.
This is an Amateur set up. A professional installer quoted me $13,000, and another quoted me $5000 to set this up. I am on a budget so took a pass on the professional install and pretty much cost of materials and some labor for digging trenches that I am supervising. Any advice on the slope issue would be appreciated.

Zone 3 has four-MP rotators MP 2000 spraying from the bottom to the top of slope, and Zone 4 has four- MP rotators MP2000 spraying from the top of the slope to the bottom. Zone 5 is blank right now, I haven't tapped into the drip line (waiting to figure out where plants going to go)

If you have a sloped property and are going to use antisyphon valves, then those valves get located at the property's high point, even if that puts a hundred feet or more between the supply connection and the valves. Antisyphon valves must be higher than any pipe or head that they feed. This is not subject to negotiation. This is code. This is law.